FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] This gene encodes a protein that appears to be a component the radial spoke head, as determined by homology to similar proteins in the biflagellate alga Chlamydomonas reinhardtii and other ciliates. Radial spokes, which are regularly spaced along cilia, sperm, and flagella axonemes, consist of a thin 'stalk' and a bulbous 'head' that form a signal transduction scaffold between the central pair of microtubules and dynein. Mutations in this gene cause primary ciliary dyskinesia 1, a disease arising from dysmotility of motile cilia and sperm. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Sep 2009]